1. Field of the Invention
The present invention relates to improved semi-allogeneic immunogenic cells which act to stimulate and induce an immunological response when administered to an individual. In particular, it relates to cells which express both allogeneic and syngeneic MHC determinants and which also express at least one antigen recognized by T lymphocytes. The invention is also directed to methods of inducing an immune response and methods of treating tumors by administering the semi-allogeneic immunogenic cells to an individual.
2. State of the Prior Art
T lymphocytes recognize an extraordinarily wide array of relatively small peptides derived from larger macromolecules in the context of membrane-associated structures specified by the class-I major histocompatibility complex (MHC).
Most progressively growing neoplastic cells form potential immunogenic tumor associated antigens (TAAs). TAAs have been identified for a number of tumors, including melanoma, breast adenocarcioma, prostatic adenocarcinoma, esophageal cancer, lymphoma, and many others. See review by Shawler et al. Advance in Pharmacology 40:309-337, Academic Press (1997). Like other epitopes, TAAs on tumor cells are recognized by T lymphocytes in the context of MHC-specified determinants. Traversari et al. (1992) J Exo. Med. 176:1453-1457; van der Bruggen et al. (1991) Science 2:1643-1647. However, such tumor cells do not provoke anti-tumor immune responses that are capable of controlling the growth of malignant cells. Boon et al. (1992) Cancer Surveys 13:23-37; Boon, T. (1993) Int. J. Cancer 54:177-180; Boon, T. (1992) Advances Cancer Res. 58:177-209.
In recent years, attention has focused on the use of cytokines in an attempt to augment the immune response to tumor-associated antigens. Cytokines such as interleukin 2 (IL-2) or interferon (IFN-.gamma.) have been used to treat neoplastic disease with marginal therapeutic impact. Vieweg et al. (1995) Cancer Investigation 132(2):193-201. Cytokines do not exhibit direct toxic effect on cancer cells; their anti-tumor activity is mediated by modulation of the host's immunological response to the neoplasm. For example, interferon-.gamma. induces the expression of MHC class I determinants and augments the sensitivity of tumor cells to cytotoxic T cell-mediated lysis. Lichtor et al. (1995) J. Neurosurg 83:1038-1044. IL-2 is required for the growth of cytotoxic T lymphocytes and enhances natural killer (NK) and lymphokine-activated killer cells (LAK). The limited effect of systemic administration of IL-2 in cancer immunotherapy has been partially explained by the short half-life of IL-2 and severe toxicity due to necessary high doses. Vieweg et al. (1995).
Lymphokine-activated killer cells (LAK) have also been used as an approach to elicit a cellular immune response. LAK cells are MHC-unrestricted lymphoid cells which kill fresh tumor cells but not normal cells. Tumor-infiltrating lymphocytes (TIL) are predominantly MHC-restricted T cells which have been found to be 50-100 times more potent than LAK cells in murine models. The use of LAK or TIL either alone or with IL-2 has shown some anti-tumor effects. In the combined approach however, IL-2 toxicity remains a problem. Vieweg et al. (1995).
More recently, immunotherapy of neoplastic disease has involved the introduction of genes for cytokines into autologous malignant cells which are then introduced into immunocompetent recipients. The introduction and expression of the gene for IL-2 or IFN-.gamma. into a tumor cell, usually by retroviral transduction, results in recognition of the cells by the immune system, a decrease in the cells' metastatic properties and the generation of immune responses that are capable of causing the rejection of both cytokine-secreting and the original cytokine non-secreting tumor cells. As occurs with other therapeutic strategies, elimination of the entire neoplastic cell population is often incomplete and tumor growth recurs. Cohen et al. (1994) Seminars in Cancer Biology 5:419-428.
In related studies, the introduction of genes specifying defined, but allogeneic (foreign to the recipient) MHC class I determinants into murine tumor cells leads to a loss of the cells' tumorigenicity in immunocompetent recipients. Similar to tumor cells which have been modified for cytokine secretion, mice rejecting tumor cells expressing both syngeneic and allogeneic antigens express immunity toward unmodified neoplasms expressing syngeneic determinants alone. Survival of tumor-bearing mice immunized with the modified cells is significantly longer than that of nonimmunized mice, although in most instances, tumor growth recurs and the animals eventually succumb to the disease. Itaya et al. (1987) Cancer Res. 47:3136-3140; Hui et al. (1989) J. Imunol. 143:3835-43; Ostrand-Rosenberg (1991) Int. J. Cancer [Suppl] 6:61-8.
Modification of tumor cells for purposes of immunotherapy requires establishment of a cell line from the patient's malignant cells. Establishing such a cell line cannot always be accomplished, as is shown by, e.g., Oettgen, et al., Immunol. Allergy. Clin. North. Am. 10:607-637 (1990). In addition, malignant cells isolated from a patient which are capable of growing in vitro may not be reflective of the patient's neoplasm as a whole. That is, tumor associated antigens present on only a small population of cells may not be included in cells which are capable of growing in vitro. Moreover, in those rare instances where a long term malignant cell line can be established, transduction of cell lines and post transduction selection can result in selective loss of tumor associated antigens expressed by the parental malignant cells in vivo.
Recent studies in cancer immunotherapies have involved the use of allogeneic cells such as mouse fibroblasts which have been genetically engineered to express (antibody-defined) melanoma-associated antigens (MAAs) and to secrete IL-2. Mice with established melanoma and immunized with the modified fibroblasts develop strong cellular anti-melanoma immune responses, mediated primarily by CD8.sup.+ T-cells, macrophages and natural killer/lymphokine-activated killer (NK/LAK) cells. Immunized mice survive significantly longer than both nonimmunized mice and mice immunized with irradiated melanoma cells. Kim et al. (1992) Int. J. Cancer 51:283-289.
Two nonexclusive mechanisms have been proposed to explain the improved response against autologous tumors in mice immunized with allogeneic cells engineered to secrete IL-2 and express MAAs:(i) large numbers of CTLs with specificity toward tumor-associated antigens expressed by the neoplasm are generated in the micro environment of allograft recognition and rejection (the immunogenic properties of tumor cells transfected with genes specifying allogenic determinants is supportive, Hui et al. (1989) J. Immunol. 143:3835-3843; Ostrand-Rosenberg et al. (1991) J. Cancer 6:[Suppl.]:61-680); and (ii) allogeneic MHC class I determinants present tumor-associated T-cell epitopes directly to CTL precursors. The high, local environment of IL-2, secreted by the genetically modified cells, further augments the generation of large numbers of CTLs with anti-tumor specificity.
Although survival of tumor-bearing mice treated with IL-2 secreting, TAA expressing, allogeneic cells is significantly (P&lt;0.001) longer than that of untreated mice, in most instances the tumor cell population is incompletely eradicated and the mice eventually die from progressive malignant melanoma. Kim et al. (1994) Cancer Immunol. Immunother. 38:185-193. The state of gene therapy is generally assessed by Roth and Cristiano, J. National Cancer Institute 89(1): 21-39 (1997), however, significant obstacles in cancer immunotherapy have yet to be overcome.
Accordingly, there is a need for more effective cellular immunogenic cells which elicit stronger and longer lasting T-cell mediated immune responses against cancerous cells in the body.